TOP ＞ シンポジウム

シンポジウム Therapeutic targets and strategies for Alzheimer’s and Parkinson’s diseases. 2S1-1 Phosphorylation controls neprilysin cell surface localization and extracellular Aβ level Kakiya Naomasa Proteolytic Neu. Sci., RIKEN BSI. Sci. Inst. Neprilysin is one of the major amyloid β peptide（Aβ）degrading enzymes. Expression of neprilysin in the brain declines during aging, leading to a metabolic imbalance of Aβ, which can induce the amyloidosis underlying Alzheimer’s disease（AD）. Pharmacological activation of neprilysin during aging is a potential way to prevent AD. However, the regulatory mechanisms of neprilysin activity in the brain still remain unclear. To address this issue, we screened for pharmacological regulators of neprilysin activity and found that the neurotrophic factors brain derived neurotrophic factor（BDNF）, nerve growth factor（NGF）, neurotrophin（NT）-3 and 4 reduce cell surface neprilysin activity. The reduction of neprilysin activity was mediated by MEK/ERK signaling which enhanced phosphorylation at serine 6（S6）in the intracellular domain of neprilysin（NEP-ICD）. Increased phosphorylation of S6-NEP-ICD reduced cell surface neprilysin and subsequently led to an increase in extracellular Aβlevels in primary neurons. Further, a specific inhibitor of protein phosphatase-1a（PP1a）tautomycetin, induced extensive phosphorylation of S6-NEP-ICD and consequently reduced cell surface neprilysin activity. Accordingly, activation of PP1a elevated cell surface neprilysin activity and lowered Aβlevels. These results together indicate that the phosphorylation state of S6-NEP-ICD influences localization of neprilysin and affects extracellular Aβ levels. Therefore, maintaining S6-NEP-ICD dephosphorylated through either inhibition of protein kinases involved in the phosphorylation at S6-NEP-ICD or by activating phosphatases catalyzing dephosphorylation of S6-NEP-ICD may represent a new way to prevent reduction of cell surface neprilysin activity during aging and to maintain a physiological level of Aβ in the brain. 2S1-2 Neuroprotective function of DJ-1 in Parkinson’s disease. Takahashi-Niki Kazuko，Ariga Hiroyoshi Grad. Sch. of Pharm. Sciences, Univ. of Hokkaido Parkinson’s disease（PD）occurs in approximately 1% of the population over the age of 65 years, the second most common neurodegenerative disease after Alzheimer’s disease. PD is a progressive neurodegenerative disease that results from dopaminergic neuronal cell death in the substantia nigra. The cause of this selective cell death is poorly understood. PD is comprised of sporadic and familial forms. Although familial PD cases account for about 10% of total cases of PD, investigations of the functions of familial PD gene products have provided great insights into the molecular mechanisms of the onset of PD, and familial PD gene products are thought to also play roles in the pathogenesis of sporadic PD. From these insights, major causes of neurodegeneration in PD are thought to be oxidative stress and mitochondrial dysfunction. The DJ-1 gene has been identified by us as a novel oncogene that transforms mouse NIH3T3 cells in cooperation with activated ras in 1997. In 2003, Bonifati et al. found a large deletion and missense mutation in the DJ-1gene as a causative gene for familial PD park7 with recessive inheritance. Although genetic and environmental factors suggest that DJ-1 affects the onset of PD, precise mechanisms at the molecular level have not been elucidated. The DJ-1 gene is a causative gene for not only familial PD（park7）but also an oncogene. DJ-1 has various functions, including transcriptional regulation, anti-oxidative stress reaction, protease and mitochondrial regulation, and its activity is regulated by its oxidative status, mainly that of cysteine 106（C106）of DJ-1. Excess oxidation of DJ-1 has been observed in patients with sporadic PD, Alzheimer’s and Huntington’s disease, suggesting that DJ-1 also participates in the onset and pathogenesis of sporadic PD as well as familial PD. DJ-1 is also a stress sensor and its expression is increased upon various stresses, including oxidative stress. In this session, I introduce functions of DJ-1 against oxidative stress and possible roles of DJ-1 in the pathogenesis of PD. 2S1-3 Histone deacetylase mediates the decrease in drebrin cluster density induced by amyloid beta oligomers. Ishizuka Yuta1，Shimizu Hideo1,2，Shirao Tomoaki1 1Department of Neurobiology and Behavior, Gunma University Graduate School of Medicine，2Laboratory of Neuropharmacology, Division of Pharmacology, National Institute of Health Sciences Dendritic spine defects are found in a number of cognitive disorders, including Alzheimer’s disease（AD）. Amyloid beta（Aβ）toxicity is mediated not only by the fibrillar form of the protein, but also by the soluble oligomers（Aβ -derived diffusible ligands, ADDLs）. Drebrin is an actin-binding protein that is located at mature dendritic spines. Because drebrin expression is decreased in AD brains and in cultured neurons exposed to Aβ, it is thought that drebrin is closely associated with cognitive functions. Recent studies show that histone deacetylase（HDAC）activity is elevated in the AD mouse model, and that memory impairments in these animals can be ameliorated by HDAC inhibitors. In addition, spine loss and memory impairment in HDAC2 over-expressing mice are ameliorated by chronic HDAC inhibitor treatment. Therefore, we hypothesized that the regulation of histone acetylation/deacetylation is critical to synaptic functioning. In this study, we examined the relationship between HDAC activity and synaptic defects induced by ADDLs using an HDAC inhibitor, suberoylanilide hydroxamic acid（SAHA）. We show that ADDLs reduce the cluster density of drebrin along dendrites without reducing drebrin expression. SAHA markedly increased the acetylation of histone proteins, and it simultaneously attenuated the ADDL-induced decrease in drebrin cluster density. In comparison, SAHA treatment did not affect the density of drebrin clusters or dendritic protrusions in control neurons. Therefore, SAHA likely inhibits ADDL-induced drebrin loss from dendritic spines by stabilizing drebrin in these structures, rather than by increasing drebrin clusters or dendritic protrusions. Taken together, our findings suggest that HDAC is involved in ADDL-induced synaptic defects, and that the regulation of histone acetylation plays an important role in modulating actin cytoskeletal dynamics in dendritic spines under cellular stress conditions, such as ADDL exposure. 2S1-4 Gaucher disease model in medaka displays axonal accumulation of alpha-synuclein Uemura Norihito，Takahashi Ryosuke Department of Neurology, Kyoto University Graduate School of Medicine Background：Recent genetic studies have revealed that mutations in glucocerebrosidase（GBA）, a causative gene of Gaucher disease（GD）, are a strong risk for Parkinson’s disease（PD）. Accrding to a previous report, the odds ratio for any GBA mutation in patients versus controls was 5.43. However, its pathological mechanisms leading to PD remain largely unknown. Medaka（Oryzias latipes）are a versatile vertebrate animal model for disease research. So far, we have reported genetic PD models of medaka that develop locomotor dysfunction accompanied by the selective loss of dopaminergic and noradrenergic neurons. Medaka have the potential to be a new animal model of PD.Objective：The objective of this study was to investigate how GBA mutations cause PD. Methods：We generated GBA mutant medaka by screening a targeting induced local lesions in genomes（TILLING）library and alpha-synuclein（α-syn）deletion mutant medaka by transcription activator-like effector nucleases（TALENs）. Results：We generated GBA nonsense mutant（GBA-/-）medaka completely deficient in glucocerebrosidase（GCase）activity. In contrast to the perinatal death of human and mice lacking GCase activity, GBA-/- medaka survived for months, enabling us to analyze disease progression. GBA-/- medaka displayed non-selective neuronal cell death accompanied by neuroinflammation, lysosomal abnormalities and α-syn accumulation in spheroids containing autophagosomes. Unexpectedly, disruption of α-syn did not improve the life span, spheroid formation, neuronal loss, or neuroinflammation in GBA-/- medaka. Conclusion：GBA-/- medaka display not only the phenotypes resembling human neuronopathic GD but also axonal accumulation of α-syn accompanied by impairment of the autophagy-lysosome pathway. Furthermore, the present study demonstrates this α-syn accumulation has minimal contribution to the pathogenesis of neuronopathic GD in medaka.